Structure of nephron and functions of its parts
- 1. Structure Of Nephron And Functions Of Its Parts
- 2. Nephron Nephron, structural and functional unit of the kidney. The word nephron is derived from the Greek word nephros, meaning kidney. They are the microscopic structure composed of a renal corpuscle and a renal tubule. There are about millions of nephrons in each human kidney. The structure that actually produces urine in the process of removing waste and excess substances from the blood.
- 4. Structure of Nephron The mammalian nephron is a long tube-like structure, its length varying from 35–55 mm long. At one end, the tube is closed, folded and expanded, into a double-walled, a cuplike structure called the Bowman’s capsule or renal corpuscular capsule, which encloses a cluster of microscopic blood vessels called the glomerulus. This capsule and glomerulus together constitute the renal corpuscle. The structure of nephron comprises two major portions: 1) Renal Corpuscle. 2) Renal Tubule.
- 5. Renal Corpuscle The renal corpuscle consists of a glomerulus surrounded by a Bowman’s capsule. The glomerulus arises from an afferent arteriole and empties into an efferent arteriole. The smaller diameter of an efferent arteriole helps to maintain high blood pressure and increases the hydrostatic pressure in the glomerulus.
- 6. Glomerulus The main function of the glomerulus is to filter plasma to produce glomerular filtrate, which passes down the length of the nephron tubule to form urine.
- 7. Bowman's capsule Bowman's capsule surrounds the glomerular capillary loops and participates in the filtration of blood from the glomerular capillaries. Bowman's capsule also has a structural function and creates a urinary space through which filtrate can enter the nephron and pass to the proximal convoluted tubule.
- 8. Renal Tubule The renal tubule is a long and convoluted structure that emerges from the glomerulus and can be divided into three parts based on function. The first part is called the proximal convoluted tubule (PCT) due to its proximity to the glomerulus; it stays in the renal cortex. The second part is called the loop of Henle or nephritic loop because it forms a loop (with descending and ascending limbs) that goes through the renal medulla. The third part of the renal tubule is called the distal convoluted tubule (DCT) and this part is also restricted to the renal cortex.
- 9. Renal Tubule The major function of tubules is reabsorption and the process can either be through active transport or passive transport. In addition, secretions by tubules help in the urine formation without affecting the electrolyte balance of the body.
- 11. Proximal Convoluted Tubule (PCT) Maximum reabsorption takes place in PCT of the nephron. PCT is the region of renal tubule where reabsorption of essential substances like glucose, proteins, amino acids, a major portion of electrolytes and water takes place. PCT selectively secretes ions such as hydrogen, ammonia, and potassium into the filtrate and absorbs HCO3 – from it.
- 12. Proximal Convoluted Tubule (PCT) The proximal tubule efficiently regulates the pH of the filtrate by exchanging hydrogen ions in the interstitium for bicarbonate ions in the filtrate; it is also responsible for secreting organic acids, such as creatinine and other bases, into the filtrate. Thus, PCT maintains the electrolyte and acid-base balance of the body fluids.
- 13. Loop of Henle Loop of Henle has a descending and an ascending limb. Being parts of the same loop, both the descending and ascending limbs show different permeability. The descending limb is permeable to water but impermeable to an electrolyte, while the ascending limb is permeable to electrolytes but impermeable to water. Since the electrolytes get reabsorbed at the ascending loop of Henle, the filtrate gets diluted as it moves towards the ascending limb. But reabsorption is limited in this segment.
- 14. Distal Convoluted Tubule (DCT) Similar to PCT, DCT also secretes ions such as hydrogen, potassium, and NH3 into the filtrate while reabsorbing the HCO3 –from the filtrate. Conditional reabsorption of sodium ions and water takes place in DCT. It plays a critical role in a variety of homeostatic processes and maintains the pH and sodium- potassium level in the blood cells.
- 15. Collecting Duct Collecting duct is a long, straight tube where H+ and K+ ions are secreted to maintain the electrolyte balance of the blood. This is also the region where the maximum reabsorption of water takes place to produce concentrated urine. Renal collecting tubule collects urine from the nephrons and moves it into the renal pelvis and ureters.